This patent relates to novel blends of chloroprene polymers which are especially useful as components of latex adhesive formulations.
Polychloroprene solvent-based adhesives are well-known and widely available compositions which provide excellent adhesion to a variety of substrates. Adhesive bond strengths are high and the compositions themselves exhibit outstanding chemical resistance. However, in spite of the superior properties of the adhesives, use of these compositions has declined as a result of environmental and health concerns related to the presence of substantial quantities of volatile organic solvents in the adhesive formulations. It is therefore a goal of the adhesives industry to develop alterative polychloroprene compositions which exhibit physical properties equivalent to those of the solvent based adhesives, but wherein the amount of organic solvent is substantially reduced or completely eliminated.
A number of aqueous latex adhesive systems have been utilized as replacements for the solvent based systems, but, unfortunately, most of these alternative systems do not exhibit comparable performance properties. For example, it is common for contactability, long term bond strength, and adhesion to non-porous substrates to be adversely affected. This is particularly true for adhesives used to bond polyvinyl chloride to itself or to other substrates.
Polychloroprene latex adhesive systems and solvent-based adhesive systems generally contain a single chloroprene elastomer, either a polychloroprene homopolymer or a chloroprene copolymer. See, for example U.S. Pat. Nos. 3,728,316; 3,920, 600 and co-pending U.S. patent application Ser. No. 07/986449, now U.S. Pat. No. 5,332,771. It has now been found that if certain chloroprene homopolymers or copolymers are blended with chloroprene/acrylate graft copolymers or chloroprene/methacrylate graft copolymers, latex adhesive compositions can be formulated which have excellent adhesion to polyvinyl chloride. That is, they exhibit rapid bond development and require low pressures to form a bond. In addition, the formulations are substantially free of organic solvent.